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Mutations
Permanent changes of DNA that
can be passed on to offspring if
they occur in cells that produce
gametes
Increase variation in populations
Types of mutations
1. Chromosomal
2. Genetic
1) Chromosomal
Mutations
Chromosomal mutations
include:
• Change of number
• Change of structure
Changes in Chromosomal
Number
Monosomy: individual inherits only one
homologue (one of the homologous pair)
Trisomy: individual inherits 3 homologous
chromosomes of one pair.
• Occur in plants and animals and is
generally lethal
• Happens because of a mistake in meiosis
called non-disjunction.
Nondisjunction
Non-lethal human monosomies
and trisomies
• Turner syndrome:
female with single X
chromosome
• Down syndrome
(trisomy 21): most
common, three copies
of 21 chromosome
Polyploidy
Offspring end up with more than two complete sets
of chromosomes
New zygote goes through multiple replication
events during s-phase
• Terms indicate how many sets of chromosomes
are present (triploids[3n], tetraploids[4n])
• Major evolutionary mechanism in plants (few
animals) responsible for 47% of flowering plants.
Polyploidy
Change in Chromosomal
Structure
Environmental factors (radiation, chemicals,
and viruses) can cause chromosomes to
break
When? How?
If broken ends do not rejoin in the same
pattern = structural chromosomal mutation
Chromosomal Mutations
Genetic Mutations
A permanent change in the
sequence of bases in the DNA
Consequences of Genetic
Mutations
They vary in their phenotypic consequences
depending on how protein activity is
affected.
Germ-line mutations are passed on to
offspring (raw material for evolution)
Somatic-line mutations only affect that
organism, but will not be passed on to
other generations.
Causes
Some are spontaneous (no apparent
reason)
• Rare due to DNA polymerase proofreading
new strand during DNA replication. (1 to
every 1 billion nucleotide pairs)
Some due to environmental mutagens
(increase chances).
• Examples include radiation (UV) and
organic chemicals (nicotine).
Types of Genetic Mutations
1) Point mutations: changes or
substitutions in one or a few
nucleotides in the sequence of DNA.
- usually affect a single amino acid in the
protein.
Base–pair
substitution. Mutations
are changes in DNA, but
they are represented here
as they are reflected in
mRNA and its protein
product. Base–pair
substitutions may lead to
silent, missense, or
nonsense mutations.
Types of Genetic Mutations
2) Frameshift Mutations: When a nucleotide
is either inserted or deleted from the
sequence in the DNA.
• By changing the position of codons, these
mutations may change every amino acid
the follows the mutation.
Strictly speaking, the example
at the bottom is not a point
mutation because it involves
insertion or deletion of more
than one nucleotide.
QOD
The template strand of a gene contains the
sequence 3′–TACTTGTCCGATATC–5′.
Draw the double strand of DNA and the
resulting mRNA, labeling all 5′ and 3′
ends. Determine the amino acid
sequence. Then show the same after a
mutation changes the template DNA
sequence to 3′–TACTTGTCCAATATC–5′.
What is the effect on the amino acid
sequence?
Answer
The amino acid sequence of the wild–type
protein is Met–Asn–Arg–Leu. The amino
acid sequence of the mutant protein
sequence would be the same, because
the mRNA codons 5′–CUA–3′ and 5′–
UUA–3′ both code for Leu.
This would make it a silent point mutation
DNA Technology
1)
2)
3)
4)
Science behind
Analyzing DNA molecules
Gene Regulation
Recombinant DNA Technology
1) Genetic Engineering
The direct manipulation of genes for
practical purposes.
Applications include the manufacture of
protein products (hormones, blood clotting
factors, etc.)
Biotechnology: the manipulation of
organisms or their components to make
useful products.
Biology behind genetic
engineering
Made possible by the discovery (1960’s) of
bacterial enzymes that cut DNA molecules
at a limited number of specific locations.
Restriction Enzymes: naturally occurring
bacterial enzymes that are used to protect
them from intruding DNA from other
organisms (viruses, other species of
bacteria).
• They work by cutting up the foreign DNA
or restricting their propagation
Restriction Enzymes
Work by catalyzing the hydrolytic reaction of
sugar phosphate bonds between specific
bases.
This results in DNA fragments that have
either Blunt or Sticky ends.
Ex. The restriction enzyme BAM III cuts
sugar-phosphate bonds between A and T
or visa versa.
TGATCAAGCTACG
ACTAGTTCGATGC
Sticky ends
Ex. The rest. enzy. Eco RI always cuts
sugar-phos bonds b/w G and A or visa
versa.
TGAATTCGC
ACTTAAGCG
2) Analyzing DNA
DNA fingerprinting (gel electrophoresis): the
technique of taking DNA samples, cutting
them with restriction enzymes to make
DNA fragments of different sizes, and
separating them based on their size
Used to identify:
• mutant varieties of genes,
• genetic make-up of extinct organisms,
• individual’s identity from trace evidence,
• and paternity cases
DNA Fingerprinting
Gel Electrophoresis: Technique that uses
a gel as a molecular sieve to separate
nucleic acids or proteins on the basis of
size, electrical charge, and other
properties (friction).
1.DNA samples are treated with a restriction
enzyme to cut it into fragments of different
sizes called restriction fragment length
polymorphisms (RFLP’s)
Gel Electrophoresis
2. All RFLP’s from sample inserted into a
well in a gel
3. An electrical charge is applied to the gel,
which causes RFLP’s to migrate down gel
according to length (how?
chromatography), resulting in a distinct
pattern of bands based on genetic code.
4. Gel’s have many wells so that different
samples can be analyzed side by side.
3)Eukaryotic Gene Regulation
We all begin life from a single celled zygote with a full
compliment of 46 chromosomes. Yet, through
development and mitosis, cells become specialized in
structure and function. Genes that code for digestive
enzymes are only active in digestive cells, but that
gene is still located in all of your cells; it is just turned
off.
Regulation
Regulation of metabolic
pathways can happen
by:
(a) Feedback inhibition of
actual pathway, rapid
(b) Repress the
expression of genes
that code for the
enzymes in the
pathway, long term.
Operons and Regulation
A single promoter serves all genes that code
all enzymes in a pathway.
Thus transcription will give rise to one long
mRNA for all enzymes. Has many start
and stop codons within.
Key advantage to this is having a single “onoff switch” to control many functionally
related genes.
Operons and Regulation
The “on-off switch” on DNA is called an
operator.
All together: The promoter, operator, and the
genes they control is an operon.
The operon is controlled by a protein called
a repressor.
The repressor protein is coded from a
regulatory gene located upstream of the
operon.
The trp operon (tryptophan) fig 16.1
Repressor proteins become
active by end product of path
way (tryptophan in this
example)
- This is known as a
Repressible operon
Inducible Operons
Opposite from repressible; repressor protein
keeps operon off. (AKA repressor is active
by itself)
When inducer is present, it will change
shape of repressor so that it can’t bind to
operator, thus turning operon “on”
The lac operon (lactose) fig 16.2
Lactose metabolism: inducer is
allolactose which is an isomer
of lactose.
Genome
• Genome: all of a cell’s DNA
including all genes that code for
protein product
• In eukaryotes, there is no
universal regulatory mechanism
that controls the expression of
coding genes. (as apposed to
prokaryotes)
– Regulation is possible at any
point in the pathway from
gene to functional protein
The Four Types of Regulation
1.) Transcriptional Control: which genes are
transcribed or the rate to which they are
transcribed.
– Nucleus
– Could involve organization of chromatin or the
use of transcription enzymes
The Four Types of Regulation
(Cont.)
2.) Posttranscriptional Control: after [rimary
mRNA transcript is formed.
– Nucleus
– Processing into mature mRNA, or speed with
which mature mRNA leaves the nucleus
The Four Types of Regulation
(Cont.)
3.) Translational Control:
– Cytoplasm
– How long the mature mRNA lasts in the
cytoplasm or ability to bind to ribosomes
– Possible that certain mRNA molecules may
need additional changes before translation
occurs
The Four Types of Regulation
(Cont.)
4.) Posttranslational Control:
– Cytoplasm
– Occurs after protein synthesis
– Polypeptide may have to go through
additional changes before it is biologically
functional
– Could be subject to feedback control
• Regardless of the mechanism of gene
expression in eukaryotes, there is cellular
control of the amount and activity of gene
products.
4) Recombinant DNA (rDNA)
rDNA is engineered to contain DNA from
two different sources.
To make rDNA engineers need to use a
vector.
Vectors are organisms or substances that
insert their DNA into other host organisms
Viruses or Plasmids
Plasmids are small accessory rings of bacterial DNA used
for sexual reproduction during conjugation
rDNA
To engineer rDNA, a foreign gene and a
plasmid (vector DNA) are treated with the
same restriction enzyme (one that
produces sticky ends)
The two segments are joined by using DNA
ligase.
Recombinant plasmids can be
inserted back into bacteria, to
reproduce asexually (how?)
This will make many copies of the
rDNA so we can harvest their
protein product
Recombinant plasmids can also be
inserted into other cells to
incorporate the rDNA to their
genome
Using viruses
as vector DNA
can also be
employed to
incorporate new
genes into
patients
- Gene therapy